1. Field of the Invention
The present invention relates to an improvement in electrodes of a semiconductor device in which a copper type wire is used as a bonding wire.
2. Description of the Related Art
Generally, in a high-frequency semiconductor device, an integrated circuit and the like, an electrode is formed of aluminum. The aluminum allows a bonding pad to be formed on an oxide film on a silicon substrate.
FIG. 1 is a cross-sectional view showing a conventional semiconductor device.
In FIG. 1, element 13 having a PN junction, such as a transistor, is formed in the surface region of silicon substrate 11. Oxide film 12 is formed on silicon substrate 11 and has contact hole 14 for extracting an electrode. Aluminum electrode 15 is thus extracted through contact hole 14 and allows a bonding pad to be formed on oxide film 12.
The above-described configuration of the conventional semiconductor device has a drawback wherein a stress locally concentrates directly under the bonding pad.
As illustrated in FIG. 2, semiconductor chip 16 including the above-described configuration of the conventional semiconductor device is mounted on lead frame 17. Aluminum electrode 15 is thus connected to an external lead by copper type wire 18 made of copper, copper alloy or the like. Since the wire is stiff enough to be used as a bonding wire, aluminum electrode 15 is bent to be connected to the external lead. In the conventional semiconductor device, semiconductor chip 16 is greatly damaged and crack 19 is easy to occur in oxide film 12 directly under the bonding pad or even in silicon substrate 11 under oxide film 12.
If crack 19 occurs in oxide film 12, an insulation state cannot be maintained, and a leak or a short circuit is caused between electrodes.